The invention relates generally to scintillation cameras, and more particularly to an improved scintillation camera comprising a plurality of fields of view.
Scintillation cameras are well known in the art of nuclear medicine, and are used for medical diagnostics. A patient ingests, or inhales or is injected with a small quantity of a radioactive isotope. The radioactive isotope emits photons that are detected by a scintillation medium in the scintillation camera. The scintillation medium is commonly a sodium iodide crystal BGO or other. The scintillation medium emits a small flash or scintillation of light, in response to stimulating radiation, such as from a patient. The intensity of the scintillation of light is proportional to the energy of the stimulating photon, such as a gamma photon. Note that the relationship between the intensity of the scintillation of light and the gamma photon is not linear.
A conventional scintillation camera such as a gamma camera includes a detector which converts into electrical signals gamma rays emitted from a patient after radioisotope has been administered to the patient. The detector includes a scintillator (a scintillation crystal) and an array of photomultiplier tubes. The gamma rays are directed to the scintillator which absorbs the radiation and produces, in response, a very small flash of light. The photodetectors, which are placed in optical communication with the scintillation crystal, convert these flashes into electrical signals which are subsequently processed. The SIGNAL processing enables the camera to produce an image of the distribution of the radioisotope within the patient.
Gamma radiation is emitted in all directions and it is necessary to collimate the radiation before the radiation impinges on the scintillation crystal. This is accomplished by a collimator which is a sheet of absorbing material, usually lead, perforated by relatively narrow channels. The collimator is detachably secured to the detector head, allowing the collimator to be changed to enable the detector head to be used with the different energies of isotope to suit particular characteristics of the patient study. The collimator may vary considerably in weight to match the isotope or study type.
Scintillation cameras are used to take four basic types of pictures: spot views, whole body views, partial whole body views, SPECT views, and whole body SPECT views.
A spot view is an image of a part of a patient. The area of the spot view is less than or equal to the size of the field of view of the gamma camera. In order to be able to achieve a full range of spot views, a gamma camera must be positionable at any location relative to a patient.
One type of whole body view is a series of spot views fitted together such that the whole body of the patient may be viewed at one time. Another type of whole body view is a continuous scan of the whole body of the patient A partial whole body view is simply a whole body view that covers only part of the body of the patient. In order to be able to achieve a whole body view, a gamma camera must be positionable at any location relative to a patient in an automated sequence of views
The acronym xe2x80x9cSPECTxe2x80x9d stands for single photon emission computerized tomography. A SPECT view is a series of slice-like images of the patient. The slice-like images are often, but not necessarily, transversely oriented with respect to the patient. Each slice-like image is made up of multiple views taken at different angles around the patient, the data from the various views being combined to form the slice-like image, In order to be able to achieve a SPECT view, a scintillation camera must be rotatable around a patient, with the direction of the detector head of the scintillation camera pointing in a series of known and precise directions such that reprojection of the data can be accurately undertaken.
A whole body SPECT view is a series of parallel slice-like transverse images of a patient Typically, a whole body SPECT view consists of sixty four spaced apart SPECT views. A whole body SPECT view results from the simultaneous generation of whole body and SPECT image data. In order to be able to achieve a whole body SPECT view, a scintillation camera must be rotatable around a patient, with the direction of the detector head of the scintillation camera pointing in a series of known and precise directions such that reprojection of the data can be accurately undertaken.
Therefore, in order that the radiation detector be capable of achieving the above four basic views, the support structure for the radiation detector must be capable of positioning the radiation detector in any position relative to the patient. Depending an the type of study being conducted, the configuration of the radiation detector is variable. The two common types of studies are planar imaging and cardiac imaging.
Planar imaging is used for bone scanning and various other types including liver scanning. In order to obtain optimum images, two cameras should be opposed one another. In general, these cameras should also be relatively large in order to obtain a large field of view.
Cardiac imaging is used for obtaining images of the heart. In order to obtain optimum images, two detector heads and two collimators should be at substantially 90 degrees to one another; with their fields of view as close as possible.
In an attempt to provide the ability to produce both types of images with a single scintillation camera, detectors of variable geometry were developed. These systems conduct both planar and cardiac imaging However, the problem with these systems is that it is difficult, if not impossible, to position the heads to the exact same position where a prior image was taken from. This is primarily due to backlash in the mechanical structure of the system. When the computer conducts the reconstruction of the images, it does so with the assumption that the information it is writing into the pixels in the image display is in the correct place. With the presence of backlash, the computer is unknowingly writing information into the wrong place, which results in blurring of the image and loss of image resolution. This in turn results in images that are inaccurate. This also precludes any reproducibility of the study.
Also, these systems use two separate and distinct detectors to produce the 90 degrees view. This means that it further requires lead shielding between the detectors to prevent any stray radiation from getting into each of the detectors With the lead shielding between the detectors, the detectors are prevented from being as close together as possible in the 90 degree position; they are not as close as they would be without the shielding between them. Since then, the fields of view of the detectors are not close as desired, this leaves open the risk of cutting off views of the heart as cardiac imaging is conducted.
These systems also, generally, cannot easily vary in size of support to accommodate different sizes of patients. In order to accommodate either a larger or smaller patient, the entire scintillation camera must be physically repositioned.
The use of three detectors is known, but usually, these systems use three relatively small detectors in the viewing area. The smaller fields of view of the detectors mean they cannot produce whole body images or images of the skeleton.
Even if the system did utilize relatively large detectors, systems using three relatively large detectors have disadvantages. The detectors are generally set at 60 degrees from one another, and when large detectors are placed in this configuration, the distance from the detector head to the patient is undesirably large. To overcome this, the detectors are required to slide over one another. As well, a 60 degrees setting is not ideal for cardiac work. As mentioned above, the image should be taken at 90 degrees.
Therefore, there is a need for a scintillation camera with a great versatility, which can be used for both planar and cardiac imaging, and can mitigate the problems and disadvantages of the prior art camera.
According to one aspect of the invention, there is provided a scintillation camera having at least one dual scintillation detector head. The scintillation camera comprises (a) a first scintillation detector head, the first scintillation detector head being a dual scintillation detector head which comprises two scintillation detectors fixed relative to each other in the form of V-shape, (b) a second scintillation detector head spaced from the first scintillation detector head such that a portion of a patient""s body may be placed in the fields of view provided by at least the first scintillation detector head, and (c) a mechanism for supporting the first and second scintillation detector heads in selected positions relative to each other and to the portion of the patient""s body when in use. The supporting mechanism is adapted to position the first and second scintillation detector heads such that a portion of a patient""s body may be located between the first and second scintillation detector heads.
The second scintillation detector head preferably includes a dual scintillation detector head or a single scintillation detector head. In the dual scintillation detector head, the two scintillation detectors are substantially at 90 degrees to each other.
The supporting mechanism preferably comprises an annular support defining at the center thereof a patient cylinder where the patient is positioned along the longitudinal axis of the patient cylinder, and a pair of mounding structures for mounting the first and second scintillation detector heads on the annular support. The annular support can be rotatable about the longitudinal axis of the patient cylinder. The first and second scintillation detector heads are rotatably supported by the mounting structures about two individual supporting axes respectively, which are vertical to the longitudinal axis of the patient cylinder. The two supporting axes are parallel to each other.
The first and second scintillation detector heads are preferably supported on the annular support in opposed relation to each other, typically, in symmetrically opposed relation to each other.